A variety of different hosts including plants, algae, fungi, stramenopiles and yeast are being investigated as means for commercial polyunsaturated fatty acid [“PUFA”] production. Genetic engineering has demonstrated that the natural abilities of some hosts (even those natively limited to linoleic acid [LA; 18:2 ω-6] and α-linolenic acid [ALA; 18:3 ω-3] fatty acid production) can be substantially altered to result in high-level production of various long-chain ω-3/ω-6 PUFAs. Whether this is the result of natural abilities or recombinant technology, production of arachidonic acid [ARA; 20:4 ω-6], eicosapentaenoic acid [EPA; 20:5 ω-3] and docosahexaenoic acid [DHA; 22:6 ω-3] may all require expression of a Δ6 desaturase.
Most Δ6 desaturase enzymes identified thus far have the primary ability to convert LA to γ-linolenic acid [GLA; 18:3 ω-6], with secondary activity in converting ALA to stearidonic acid [STA; 18:4 ω-3]. Based on the role Δ6 desaturase enzymes may play in the synthesis of e.g., ARA, EPA and DHA, there has been considerable effort to identify and characterize these enzymes from various sources. As such, numerous Δ6 desaturases have been disclosed in both the open literature (e.g., GenBank) and the patent literature (e.g., U.S. Pat. Nos. 5,968,809, 7,067,285, and 7,335,476 and U.S. Pat. Appl. Pub. No. 2006-0117414). Along with Δ5, Δ8 and Δ4 desaturases, Δ6 desaturases are known as long-chain PUFA “front-end” desaturases (wherein desaturation occurs between a pre-existing double bond and the carboxyl terminus of the fatty acid's acyl group, as opposed to methyl-directed desaturation). These desaturases are characterized by three histidine boxes [H(X)3-4H (SEQ ID NOs:3 and 4), H(X)2-3HH (SEQ ID NOs:5 and 6) and H/Q(X)2-3HH (SEQ ID NOs:7 and 8)] and are members of the cytochrome b5 fusion superfamily, since they possess a fused cytochrome b5 domain at their N-terminus which serves as an electron donor.
Although genes encoding Δ6 desaturases are known, there is a need for additional varieties of these enzymes with varying enzymatic properties that are suitable for heterologous expression in a variety of host organisms for use in the production of ω-3/ω-6 fatty acids. Applicants have addressed the stated need by isolating genes encoding Δ6 desaturases from the red alga, Porphyridium cruentum. 